1. Field of the Invention
The present invention relates to a semiconductor device preventing a poor connection or the like caused by a step or the like in a case that a conductive film and an insulating film, or a semiconductor film or the like are stacked, and a manufacturing method of the semiconductor device.
2. Description of the Related Art
In recent years, thin film transistors (TFTs) have been formed over a substrate having insulating surfaces, such as glass substrates, and semiconductor devices which use the thin film transistors as switching elements or the like are manufactured actively. The thin film transistors are formed so that island-shaped semiconductor films are formed over substrates having insulating surfaces by using CVD, etching or the like, and the island-shaped semiconductor films are used as channel regions of transistors. (for example, Patent Document 1: Japanese patent Laid-Open No. Hei 08-018055)
A general manufacturing method of a thin film transistor is shown in FIG. 17A to 17E. First, a semiconductor film 950 is formed over a substrate 951 with an insulating film 957 which functions as a base film therebetween (FIG. 17A). Next, the semiconductor film 950 is removed selectively and island-shaped semiconductor films 955 are formed (FIG. 17B), and a gate insulating film 956 is formed to cover the island-shaped semiconductor films 955 (FIG. 17C). Gate electrodes 953 are formed selectively over the island-shaped semiconductor films 955 with the gate insulating film 956 therebetween (FIG. 17D). Then, an n-channel thin film transistor 952a and a p-channel thin film transistor 952b are formed by forming insulating films (side walls) so as to contact with side surfaces of the gate electrodes and introducing an impurity element which shows a p-channel or an n-channel selectively or forming a source region, a drain region and an LDD region (FIGS. 17E and 18A).
Thus, the thin film transistor can be formed over the substrate through a process shown in FIGS. 17A to 17E. FIGS. 17A to 17E shows a cross-sectional structure between a-b of FIG. 18A.    [Patent Document 1]    Japanese patent Laid-Open No. Hei 08-018055